The present invention relates to the installation of elongate conduits into a submerged earth formation from an offshore tower.
The recovery of fluids, such as oil, from offshore subterranean formations typically involves establishing a plurality of offshore wells which extend into the water bed from a tower situated in the body of water. Normally each well is constructed by driving an elongate drill conductor into the water bed, clearing the conductor interior of mud, then inserting a drill string through the conductor and drilling the well. This technique has been progressively improved with a view toward enabling a plurality of wells to emanate from a single offshore tower and attain as wide a lateral reach into the oil formation as possible. In this fashion, oil exploration and recovery operations are maximized.
Previously proposed efforts toward this end involved linearly installing the conductors at an angle relative to vertical and conducting the drilling operations by means of a slant drilling rig. (See for example, Storm U.S. Pat. No. 3,451,493.) While such an arrangement would provide conductors projecting beyond the perimeter of the tower and thus extend the lateral reach of the drill strings, the required slant drilling rigs are relatively expensive and difficult to operate.
Relatively recent proposals have been made in which it is envisioned that a conductor be installed from a tower deck by initially lowering the conduit vertically downwardly and then gradually curving the conductor outwardly and downwardly through the tower as it approaches the floor of the water body. It has been suggested to accomplish this by progressively urging the conduit through a series of guides which deflect the conductor into a curved configuration (e.g., see Mott et al. U.S Pat. No. 3,670,507 -- June 20, 1972). Another suggestion involves plastically performing the conductor before or during installation so that the conductor is urged through the guides in a curved profile (e.g., see Marshall et al. U.S. Pat. No. 3,687,204 -- Aug. 29, 1972. Both of these suggestions involve urging a conductor downwardly through a series of guides while in a curved posture. As will be appreciated, such a procedure is accompanied by substantial resistance. This resistance must be dealt with during the entire period of descent of the conductor, which is often driven hundreds of feet into the water bed.
It would be desirable to install a conductor into the water bed to achieve a wide lateral reach while encountering less resistance and without requiring the subsequent use of a slant drilling rig.
It is therefore an object of the present invention to obviate or minimize problems such as those discussed previously.
It is also a major object of the invention to provide conductors with straight line exit paths which tend to effectively control directions of deviated drilling.
It is a further object of the invention to provide methods for installing a conductor with minimum resistance to achieve a wide lateral reach, and without requiring the subsequent use of a slant drilling rig.
It is yet another object to provide such methods wherein a portion of the conductor situated above the water bed includes an upper segment oriented in a vertically straight posture and a lower segment oriented in an inclinedly straight posture.
It is a further object of the invention to provide such methods wherein the conductor is initially installed along a straight path inclined relative to vertical, and the upper conductor segment is subsequently bent about a fulcrum to assume a vertically straight posture.
It is still a further object of the invention to provide an apparatus for supporting a conductor from an offshore tower such that the upper conductor segment is oriented in a vertically straight posture and the lower conductor segment is oriented in an inclinedly straight posture.
It is still another object of the invention to provide such an apparatus wherein the conductor is supported in guide apertures of different cross-sections, with one of the guide apertures defining a fulcrum about which the conductor is bent.